Capnography, as is well known in the art, is the measurement of the level of carbon dioxide (CO2) in exhaled or inhaled breath The information obtained from a capnographic measurement is generally presented on the display of the capnograph as a series of waveforms, representing the partial pressure of CO2 in the patient's exhaled breath as a function of time. The information can be displayed at a fast rate, in which case the fine detail of each breath can be evaluated, or at a slow rate, in which case the trend in the end tidal value of exhaled CO2 (EtCO2) can be evaluated.
Clinicians use capnography in order to assess a patient's respiratory status. Respiratory arrest and shunt can be speedily diagnosed, and a whole range of other respiratory problems and conditions can be determined by the shape and trends of the waveforms. In conjunction with other measurements, pulmonary blood flow, embolism and cardiac arrest can be assessed. Capnography is considered to be a prerequisite both for safe intubation and general anesthetic, and for correct ventilation management. Furthermore, recently proposed standards will mandate the use of capnographic monitoring of patients under sedation, even in simple everyday situations such as minor cosmetic surgical procedures, or pediatric dental surgery, or pediatric sedation for the performance of imaging procedures such as MRI.
Up to now, the interpretation of capnographic waveforms has generally been performed by the respiratory specialist or the anesthetist. Such personnel have sufficient experience to be able to perform an accurate diagnosis from an inspection of the waveforms on the monitor screen of the capnograph. However, with the increased use of capnography both by medical specialists in other fields and by paramedical personnel in emergency service environments, the capnograph operator is not always able to make a safe diagnosis of the patient's respiratory condition by observing the waveform graphs. The waveforms typically have a large number of different parameters, each of which taken by itself cam indicate a different condition, and combinations of which can indicate yet further different conditions, These conditions relate not only to the physiological state of the patient, but also to the correct operation and connection of respiratory support apparatus.
There therefore exists an important need for instrumentation which will provide diagnostic support for the capnograph operator beyond the display of the capnographic waveforms and trends on a monitor screen.